New Insights from Seismic Data into Stratal Geometries of Cretaceous Carbonate Platform Systems of the Middle East

Droste, Henk, JVR Centre Carbonate Research, Muscat, Oman

Cretaceous platform interior carbonates host major hydrocarbon accumulations in the Middle East. High-resolution 3-D seismic data, integrated with outcrop studies in Oman, show that the internal stratigraphic architecture of these systems is more complicated than previously thought. Recognition of these geometries is essential for the successful applica­tion of waterflood and Enhanced Oil Recovery techniques, as well as for the definition of stratigraphic traps. 3-D seismic data show that mounded and inclined stratal geometries are common. Clinoform angles, with dips of 0.5 – 5o, appear to be much steeper than suggest­ed in correlations based on well data only. Individual lithostratigraphic units on the platform, which from well log and core data look homogenous and laterally continuous, appear to con­sist of a number of merged intra-shelf platforms. Examples come from the Aptian Shu’aiba Formation and the Albian to Cenomanian Natih-e and a/b members. These intra-shelf plat­forms developed from scattered, small carbonate buildups that started to grow following major flooding of the platform interior. During subsequent progradation the build-ups amal­gamated into larger platforms. These observations show that the previous stratigraphic models, which were based on the correlation of 1D well and core data, are oversimplified and artificially flatten the stratigraphy, even between closely-spaced wells. This is especially the case in the upper, shallowing upward parts of the cycles. As a result, the stratigraphic trapping potential as well as the internal reservoir heterogeneity for these systems tends to be underestimated.